Plasma treating apparatus and plasma treating method

ABSTRACT

In a plasma treating apparatus for carrying out a plasma treatment over a silicon wafer  6  having a protective tape  6   a  stuck to a circuit formation face, the silicon wafer  6  is mounted on a mounting surface  3   d  which is provided on an upper surface of a lower electrode  3  formed of a conductive metal with the protective tape  6   a  turned toward the mounting surface  3   d . When a DC voltage is to be applied to the lower electrode  3  by a DC power portion  18  for electrostatic adsorption to adsorb and hold the silicon wafer  6  onto the lower electrode  3  in the plasma treatment, the protective tape  6   a  is utilized as a dielectric for the electrostatic adsorption. Consequently, the dielectric can be thinned as much as possible and the silicon wafer  6  can be held by a sufficient electrostatic holding force.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 10/227,930filed Aug. 26, 2002, now allowed.

BACKGROUND OF THE INVENTION

The present invention relates to a plasma treating apparatus and aplasma treating method in which a plasma treatment is carried out over asemiconductor substrate such as a silicon wafer.

In a process for manufacturing a silicon wafer to be used in asemiconductor device, a thinning work for reducing the thickness of asubstrate is carried out with a reduction in the thickness of thesemiconductor device. The thinning work is carried out by forming acircuit pattern on the surface of a silicon substrate, and then,mechanically polishing the back of a circuit formation face. A plasmatreatment is carried out in order to remove, by etching, a damage layergenerated on the polished surface of the silicon substrate by themechanical polishing after the polishing work.

In the plasma treatment, the silicon wafer is to be held in such anattitude that a surface to be treated (a back face) is turned upward.For this reason, the silicon wafer is held in such an attitude that thecircuit formation face side is turned toward the mounting surface of asubstrate mounting portion. At this time, a protective tape is stuckonto the circuit formation face in order to prevent a circuit from beingdamaged due to a direct contact with the mounting surface.

As a method of holding the silicon wafer, there has been known a methodusing electrostatic adsorption. In this method, the silicon wafer ismounted on a substrate mounting portion in which the surface of aconductor is coated with a thin insulating layer, a DC voltage isapplied to the conductor to cause the surface of the substrate mountingportion to be an electrostatic adsorption surface, and a coulomb forceis applied between the silicon wafer and the conductor provided underthe insulating layer, thereby holding the silicon wafer in the substratemounting portion.

In the case in which the silicon wafer having the protective tape stuckthereto is held by the electrostatic adsorption, however, the coulombforce acts with an insulating protective tape provided in addition tothe insulating layer. As compared with the case in which the siliconwafer is directly bonded hermetically to the electrostatic adsorptionsurface without the protective tape, therefore, the electrostaticadsorption force is small and a sufficient holding force cannot beobtained in some cases. Also in the case in which a resin layer isformed for sealing or wiring over the surface of the silicon wafer andthe resin layer side is hermetically bonded to the electrostaticadsorption surface to carry out the electrostatic adsorption,furthermore, the same problem arises.

SUMMARY OF THE INVENTION

Therefore, it is an object of the invention to provide a plasma treatingapparatus and a plasma treating method which can hold a semiconductorsubstrate by a sufficient electrostatic holding force to eliminate adrawback.

In a plasma treating apparatus for carrying out a plasma treatment overa silicon wafer having a protective tape stuck to a circuit formationface, the silicon wafer is mounted on a mounting surface which isprovided on an upper surface of a lower electrode formed of a conductivemetal with the protective tape turned toward the mounting surface. Whena DC voltage is to be applied to the lower electrode by a DC powerportion for electrostatic adsorption to adsorb and hold the siliconwafer onto the lower electrode in the plasma treatment, the protectivetape is utilized as a dielectric for the electrostatic adsorption.Consequently, the dielectric can be thinned as much as possible and thesilicon wafer can be held by a sufficient electrostatic holding force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a plasma treating apparatus accordingto an embodiment of the invention;

FIG. 2 is a sectional view showing the substrate mounting portion of theplasma treating apparatus according to the embodiment of the invention;

FIG. 3 is a sectional view showing the plasma treating apparatusaccording to the embodiment of the invention;

FIG. 4 is a graph showing an electrostatic adsorption force in theplasma treating apparatus according to the embodiment of the invention;

FIG. 5 is a flow chart showing a plasma treating method according to anembodiment of the invention;

FIG. 6 is a view illustrating a process for the plasma treating methodaccording to the embodiment of the invention;

FIG. 7 is a view illustrating the plasma treating method according tothe embodiment of the invention; and

FIG. 8 is a view showing the substrate mounting portion of the plasmatreating apparatus according to the embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, an embodiment of the invention will be described with reference tothe drawings. FIG. 1 is a sectional view showing a plasma treatingapparatus according to an embodiment of the invention, FIG. 2 is asectional view showing the substrate mounting portion of the plasmatreating apparatus according to the embodiment of the invention, FIG. 3is a sectional view showing the plasma treating apparatus according tothe embodiment of the invention, FIG. 4 is a graph showing anelectrostatic adsorption force in the plasma treating apparatusaccording to the embodiment of the invention, FIG. 5 is a flow chartshowing a plasma treating method according to an embodiment of theinvention, FIGS. 6 and 7 are views illustrating a process for the plasmatreating method according to the embodiment of the invention, and FIG. 8is a view showing the substrate mounting portion of the plasma treatingapparatus according to the embodiment of the invention.

First of all, the plasma treating apparatus will be described withreference to FIGS. 1 and 2. In FIG. 1, the inside of a vacuum chamber 1acts as a treatment chamber 2 for carrying out a plasma treatment, and alower electrode 3 and an upper electrode 4 are vertically opposed toeach other in the treatment chamber 2. The lower electrode 3 is attachedto the vacuum chamber 1 in an electrical insulation state through asupport portion 3 a extended downward, and furthermore, the upperelectrode 4 is attached to the vacuum chamber 1 in a conduction statethrough a support portion 4 a extended upward.

The lower electrode 3 is fabricated by a conductive metal, and the uppersurface of the lower electrode 3 has almost the same shape as the planarshape of a silicon wafer 6 (FIG. 2) which is a semiconductor substrateto be treated and acts as a mounting surface 3 d for mounting thesemiconductor substrate thereon. Accordingly, the lower electrode 3 actsas a substrate mounting portion provided with a mounting surface towhich a conductor is exposed and serving to mount the semiconductorsubstrate thereon. The silicon wafer 6 is set in a state obtainedimmediately after the back side of a circuit formation face is polishedby mechanical polishing, and a protective tape 6 a is stuck to thecircuit formation face of the silicon wafer 6 in order to protect thecircuit formation face from an impact generated during the mechanicalpolishing as shown in FIG. 2. The silicon wafer 6 is mounted on themounting surface of the mounting portion in such a state that theprotective tape 6 a side is turned toward the mounting surface 3 d ofthe lower electrode 3 and the mechanical polished surface is turnedupward. In the mounting state, an insulating layer is provided incontact with the mounting surface to be a conductor. The mechanicalpolished surface is subjected to the plasma treatment so that a damagelayer generated by the polishing work is removed.

The protective tape 6 a is a resin tape obtained by forming aninsulating resin using polyolefin, polyimide or polyethyleneterephthalate as a material into a film having a thickness ofapproximately 100 μm and is stuck to the circuit formation face of thesilicon wafer 6 with an adhesive. The protective tape 6 a stuck to thesilicon wafer 6 is an insulating layer formed on the circuit formationface (surface) and the insulating layer functions as a dielectric in theelectrostatic adsorption of the silicon wafer 6 onto the mountingsurface as will be described below.

A gate valve 1 a for substrate conveyance in/out is provided on the sidesurface of the vacuum chamber 1. The gate valve 1 a is opened and closedby a gate switching mechanism (not shown). An exhaust pump 8 isconnected to the vacuum chamber 1 through a valve opening mechanism 7.When the valve opening mechanism 7 is brought into an opening state todrive the exhaust pump 8, the inside of the treatment chamber 2 in thevacuum chamber 1 is evacuated. When an air opening mechanism 9 isbrought into an opening state, the air is introduced into the treatmentchamber 2 so that a vacuum is broken.

As shown in FIG. 2, a large number of adsorption holes 3 e opened to anupper surface are provided on the lower electrode 3 and communicate witha suction hole 3 b provided in the lower electrode 3. The suction hole 3b is connected to a vacuum adsorption pump 12 through a gas linechange-over switching mechanism 11, and the gas line change-overswitching mechanism 11 is connected to an N₂ gas feeding portion 13 anda He gas feeding portion 14 as shown in FIG. 1. By switching the gasline change-over switching mechanism 11, the suction hole 3 b can beselectively connected to the vacuum adsorption pump 12, the N₂ gasfeeding portion 13 and the He gas feeding portion 14.

When the vacuum adsorption pump 12 is driven in such a state that thesuction hole 3 b communicates with the vacuum adsorption pump 12, vacuumsuction is carried out through the adsorption hole 3 e and the siliconwafer 6 mounted on the mounting surface 3 d is subjected to the vacuumadsorption and is thus held. Accordingly, the adsorption hole 3 e, thesuction hole 3 b and the vacuum adsorption pump 12 act as vacuum holdingmeans for carrying out the vacuum suction through the adsorption hole 3e opened to the mounting surface 3 d, thereby vacuum adsorbing theplate-shaped substrate to be held on the mounting surface 3 d.

Moreover, the suction hole 3 b is connected to the N₂ gas feedingportion 13 or the He gas feeding portion 14 so that a nitrogen gas or ahelium gas can be jetted from the adsorption hole 3 e toward the lowersurface of the silicon wafer 6. As will be described below, the nitrogengas is a gas for blow to forcibly remove the silicon wafer 6 from themounting surface 3 d, and the helium gas is a gas for heat transferwhich is to be used for promoting the cooling of the silicon waferduring the plasma treatment.

A gas feeding portion 30 for plasma generation which serves to feed agas for plasma generation is connected to the treatment chamber 2 of thevacuum chamber 1 through a gas feeding control portion 31. The gasfeeding control portion 31 is constituted by a switching valve forcontrolling the supply of the gas for plasma generation to the vacuumchamber 1 and a flow control valve for controlling a flow rate. A gasmainly containing a fluorine based gas is often used as the gas forplasma generation, and it is preferable that a gas mainly containing SF₆(sulfur hexafluoride) should be used for the plasma treatment to removethe damage layer formed by the polishing work.

Moreover, a refrigerant passage 3 c for cooling is provided in the lowerelectrode 3. The refrigerant passage 3 c is connected to a coolingmechanism 10. By driving the cooling mechanism 10, a refrigerant such ascooling water is circulated in the refrigerant passage 3 c, therebycooling the lower electrode 3 and the protective tape 6 a stuck onto thelower electrode 3 of which temperatures are raised by heat generatedduring the plasma treatment. The refrigerant passage 3 c and the coolingmechanism 10 act as cooling means for cooling the lower electrode 3 tobe the substrate mounting portion.

The lower electrode 3 is electrically connected to a high frequencypower portion 17 through a matching circuit 16. By driving the highfrequency power portion 17, a high frequency voltage is applied betweenthe upper electrode 4 and the lower electrode 3 which are conducted tothe vacuum chamber 1 grounded on a grounding portion 19. Consequently, aplasma discharge is generated in the treatment chamber 2. The matchingcircuit 16 matches the impedances of a plasma discharge circuit forgenerating a plasma in the treatment chamber 2 and the high frequencypower portion 17. The lower electrode 3, the upper electrode 4 and thehigh frequency power portion 17 act as plasma generating means forgenerating a plasma to carry out the plasma treatment over the siliconwafer 6 mounted on the mounting surface.

While the example of a method of applying a high frequency voltagebetween the opposed parallel plate electrodes (the lower electrode 3 andthe upper electrode 4) has been illustrated as the plasma generatingmeans, it is also possible to employ another method, for example, amethod in which a plasma generating apparatus is provided in the upperpart of the treatment chamber 2 to feed a plasma into the treatmentchamber 2 through down flow.

Moreover, a DC power portion 18 for electrostatic adsorption isconnected to the lower electrode 3 through an RF filter 15. By drivingthe DC power portion 18 for electrostatic adsorption, a DC voltage isapplied to the lower electrode 3 as shown in FIG. 3A so that a negativeelectric charge is stored on the surface of the lower electrode 3. Inthis state, then, the high frequency power portion 17 is driven togenerate a plasma in the treatment chamber 2 as shown in FIG. 3B (see adotted portion 20 in the drawing). Consequently, a direct currentapplying circuit 21 for connecting the silicon wafer 6 mounted on themounting surface 3 d to the grounding portion 19 is formed through theplasma in the treatment chamber 2. Thus, a closed circuit forsequentially connecting the lower electrode 3, the RF filter 15, the DCpower portion 18 for electrostatic adsorption, the grounding portion 19,the plasma and the silicon wafer 6 is formed and a positive electriccharge is stored in the silicon wafer 6.

A coulomb force acts between the negative electric charge stored in thelower electrode 3 and the positive electric charge stored in the siliconwafer 6. By the coulomb force, the silicon wafer 6 is held in the lowerelectrode 3 through the protective tape 6 a to be a dielectric. At thistime, the RF filter 15 prevents the high frequency voltage of the highfrequency power portion 17 from being directly applied to the DC powerportion 18 for electrostatic adsorption. The lower electrode 3 and theDC power portion 18 for electrostatic adsorption act as electrostaticadsorbing means for holding the silicon wafer 6 to be the plate-shapedsubstrate on the mounting surface 3 d by the electrostatic adsorption.The polarity of the DC power portion 18 for electrostatic adsorption maybe reversed to be positive or negative.

With reference to FIG. 4, an electrostatic adsorption force will bedescribed. An adsorption force F obtained by the coulomb force is givenby F=½∈(V/d)², wherein ∈ represents a dielectric constant of adielectric, V represents a DC voltage to be applied and d represents athickness of the dielectric. FIG. 4 shows the relationship between anelectrostatic adsorption force and a DC voltage to be applied which isobtained in the case in which the protective tape 6 a fabricated by aresin is stuck to the silicon wafer 6 and is used as a dielectric in theelectrostatic adsorption.

Three kinds of resin materials, for example, polyolefin, polyimide andpolyethylene terephthalate are used for the protective tape 6 a andcalculation examples in which they are fabricated in a thickness of 100μm are shown in curves a, b and c, respectively. For comparison, thecurve d shows an electrostatic adsorption force which is obtained whenan alumina insulating layer is formed on a substrate mounting surface ina thickness of 200 μm and is used as a dielectric for the electrostaticadsorption to electrostatically adsorb a silicon wafer having noprotective tape.

As shown in FIG. 4, in the example of the polyolefin, the adsorptionforce is almost equal to that in the case of a conventional aluminainsulating layer. In the case in which two kinds of materials, forexample, polyimide and polyethylene terephthalate are used, a greateradsorption force than the adsorption force obtained by using the aluminainsulating layer is acquired.

More specifically, it is not necessary to form an insulating layer on alower electrode which is required for carrying out the electrostaticadsorption in the conventional plasma treating apparatus, andfurthermore, it is possible to implement an excellent adsorption force.Moreover, the protective tape is caused to directly come in contact withthe surface of the lower electrode 3 without an insulating layer such asalumina which has a low thermal conductivity. Consequently, an excellentcooling effect can be obtained and the heat damage of the protectivetape 6 a and the silicon wafer 6 can be relieved.

The plasma treating apparatus is constituted as described above. Aplasma treating method will be described below with reference to FIGS. 6and 7 in accordance with a flow in FIG. 5. In FIG. 5, first of all, thesilicon wafer 6 to be a treating object is conveyed into the treatmentchamber 2 (ST1) and is mounted on the mounting surface 3 d of the lowerelectrode 3 (a mounting step). At this time, since the silicon wafer 6is thin and flexible, a warpage is generated so that the mounting iscarried out with a clearance generated between the silicon wafer 6 andthe mounting surface 3 d in some cases as shown in FIG. 6A. Then, thegate valve 1 a is closed (ST2) and the vacuum adsorption pump 12 isdriven. As shown in FIG. 6B, consequently, vacuum suction is carried outthrough the adsorption hole 3 e and the suction hole 3 b so that thevacuum adsorption state of the silicon wafer 6 is turned ON (ST3). Asshown in FIG. 6C, thus, the silicon wafer 6 is held by the vacuumadsorption in a hermetic contact state with the mounting surface 3 d (aholding step).

Next, the exhaust pump 8 is driven to evacuate the treatment chamber 2,and the gas feeding control portion 31 is operated to feed a gas forplasma generation into the treatment chamber 2 (ST4). Then, the DC powerportion 18 for electrostatic adsorption is driven to turn ON theapplication of a DC voltage (ST5) and the high frequency power portion17 is driven to start a plasma discharge (ST6). As shown in FIG. 7(a),consequently, a plasma is generated in a space between the silicon wafer6 provided on the lower electrode 3 and the lower surface of the upperelectrode 4 so that a plasma treatment intended for the silicon wafer 6is carried out (a plasma treating step). In the plasma treatment, anelectrostatic adsorption force is generated between the lower electrode3 and the silicon wafer 6 (see FIG. 3(b)), and the silicon wafer 6 isheld in the lower electrode 3 by the electrostatic adsorption force.

Thereafter, the gas line change-over switching mechanism 11 is driven toturn OFF the vacuum adsorption (ST7) and back He introduction is carriedout (ST8). More specifically, the hold of the silicon wafer 6 in thelower electrode 3 by the vacuum suction is released and a helium gas forheat transfer is then fed from the He gas feeding portion 14 through thesuction hole 3 b and is jetted from the adsorption hole 3 e toward thelower surface of the silicon wafer 6 as shown in FIG. 7A. In the plasmatreatment, the lower electrode 3 is cooled by the cooling mechanism 10and the heat of the silicon wafer 6 having a temperature raised by theplasma treatment is transferred to the lower electrode 3 through ahelium gas to be a gas having a great heat transfer property.Consequently, the silicon wafer 6 can be cooled efficiently.

If a predetermined plasma treating time is passed and the discharge iscompleted (ST9), the supply of the back He and the gas for plasmageneration is stopped (ST10), and the vacuum adsorption is turned ONagain as shown in FIG. 7B (ST11). Consequently, the silicon wafer 6 isheld on the mounting surface 3 d by the vacuum adsorption force in placeof the electrostatic adsorption force eliminated by the completion ofthe plasma discharge.

Then, the DC power portion 18 for electrostatic adsorption is stopped toturn OFF the DC voltage (ST12), and the air opening mechanism 9 isdriven to carry out atmospheric opening in the treatment chamber 2(ST13).

Thereafter, the gas line change-over switching mechanism 11 is drivenagain to turn OFF the vacuum adsorption (ST14). Subsequently, wafer blowis carried out (ST15). More specifically, as shown in FIG. 7C, anitrogen gas is fed through the suction hole 3 b and is thus jetted fromthe adsorption hole 3 e. Consequently, the silicon wafer 6 is removedfrom the mounting surface 3 d of the lower electrode 3. Next, when thegate valve 1 a is brought into an opening state (ST16) and the siliconwafer 6 is conveyed to the outside of the treatment chamber 2 (ST17),the wafer blow is turned OFF (ST18) and one cycle for the plasmatreatment is ended.

As described above, in the plasma treatment according to the embodiment,a plasma is generated in the treatment chamber 2 so that the siliconwafer 6 is held in the lower electrode 6 by the vacuum adsorption beforethe electrostatic adsorption force is generated. Also in the case inwhich a thin and flexible plate-shaped substrate such as the siliconwafer 6 is intended, the silicon wafer 6 can be always bondedhermetically to the mounting surface 3 d of the lower electrode 3 andcan be thus held properly. Accordingly, it is possible to prevent anabnormal discharge from being caused in a clearance between the uppersurface of the lower electrode 3 and the lower surface of the siliconwafer 6 in the case of a hermetic bonding failure and the silicon wafer6 from being overheated due to a cooling failure.

In place of the lower electrode 3 in which the whole range of themounting surface 3 d is formed of a conductor, a lower electrode 3′shown in FIG. 8 may be used as a lower electrode. In this example, asshown in FIG. 8A, an insulating portion 3′f having a predetermined widthis formed in an outer edge portion in which a mounting surface 3′d islarger than the silicon wafer 6 to be the semiconductor substrate and isprotruded from the size of the silicon wafer 6. The insulating portion3′f is formed of ceramic such as alumina and a planar shape thereof isdetermined depending on the shape of a silicon wafer to be mounted onthe mounting surface 3′d. FIGS. 8B and 8C show an example of the shapeof the insulating portion 3′f in each of the case in which there is nooriental flat indicating the direction of the silicon wafer and the casein which there is the oriental flat.

By using such a lower electrode 3′, it is possible to obtain anadvantage that a conductor provided on the upper surface of the lowerelectrode 3′ is not directly exposed to a plasma with the silicon wafermounted and a plasma discharge can be generated more uniformly over themounting surface of the lower electrode 3′.

While the example in which the resin protective tape 6 a stuck to thesilicon wafer 6 is the dielectric for the electrostatic adsorption asthe insulating layer has been described in the embodiment, it ispossible to hermetically bond, to the mounting surface, an insulatingresin layer formed to seal the circuit formation face of the siliconwafer or an insulating resin layer provided to form another wiring layeron the circuit formation face and to utilize the insulating resin layeras the dielectric for the electrostatic adsorption.

According to the invention, the mounting surface of the substratemounting portion is caused to be a conductor and the semiconductorsubstrate is mounted with the insulating layer side turned toward themounting surface, and the insulating layer of the semiconductorsubstrate is utilized as the dielectric for the electrostatic adsorptionto electrostatically adsorb the semiconductor substrate onto themounting surface. Consequently, the semiconductor substrate can be heldby a sufficient electrostatic holding force.

1. A plasma treating apparatus for carrying out a plasma treatment overa semiconductor substrate having an insulating layer on a surface,comprising: a substrate mounting portion provided with a mountingsurface having a conductor exposed to at least a part thereof andserving to mount the semiconductor substrate with an insulating layerside turned toward the mounting surface; electrostatic adsorbing meansfor holding the semiconductor substrate on the mounting surface byelectrostatic adsorption; and plasma generating means for generating aplasma in order to treat the semiconductor substrate mounted on themounting surface, wherein said insulating layer of the semiconductorsubstrate is utilized as a dielectric for the electrostatic adsorption.2. The plasma treating apparatus according to claim 1, wherein theinsulating layer is a resin tape stuck to the surface of thesemiconductor substrate.
 3. The plasma treating apparatus according toclaim 2, wherein a material of the resin tape is one of polyolefin,polyimide and polyethylene terephthalate.
 4. The plasma treatingapparatus according to claim 1, wherein the semiconductor substrate is asilicon wafer having a circuit formation face and the insulating layeris a protective tape for protecting the circuit formation face.
 5. Theplasma treating apparatus according to claim 4, wherein a material ofthe protective tape is one of polyolefin, polyimide and polyethyleneterephthalate.
 6. The plasma treating apparatus according to claim 1,wherein the semiconductor substrate is a silicon wafer having a circuitformation face and the insulating layer is an insulating resin layerformed to seal the circuit formation face.
 7. The plasma treatingapparatus according to claim 1, wherein the semiconductor substrate is asilicon wafer having a circuit formation face and the insulating layeris an insulating resin layer provided to form a wiring layer on thecircuit formation face.
 8. The plasma treating apparatus according toclaim 1, further comprising vacuum holding means for vacuum adsorbingthe semiconductor substrate by vacuum suction through an adsorption holeopened to the mounting surface and holding the semiconductor substrateon the mounting surface, the semiconductor substrate being held on themounting surface by the vacuum holding means before a plasma isgenerated by at least the plasma generating means.
 9. The plasmatreating apparatus according to claim 1, further comprising coolingmeans for cooling the substrate mounting portion.
 10. The plasmatreating apparatus according to claim 8, further comprising heattransfer gas feeding means for feeding a gas for heat transfer to theadsorption hole.
 11. The plasma treating apparatus according to claim 1,wherein the mounting portion includes a larger mounting surface than thesemiconductor substrate, a portion of the mounting surface to which aconductor is exposed is provided in a central part of the mountingsurface, and an outer edge portion protruded from the semiconductorsubstrate on an outside thereof is formed of an insulator.